evdev: create sysctl entries before cdev to close userspace race

[ericbsd]

evdev_register_common() was creating the character device before registering the kern.evdev.input.N.* sysctl entries. The moment the cdev appears, devd fires a CREATE event for /dev/input/eventN, and userspace libraries (e.g. libudev-devd) immediately call sysctlbyname("kern.evdev.input.N.name") to enumerate device capabilities. With the old ordering, that call could arrive before the sysctl tree was populated, causing it to fail. The result was that the device was not recognised by the input stack, leaving keyboards and other HID devices non-functional after plug-in or resume from suspend.

Fix the race by calling evdev_sysctl_create() before evdev_cdev_create(). On cdev failure, free the already-registered sysctl context with sysctl_ctx_free() to avoid leaking it.

Summary by Sourcery

Fix evdev device registration ordering to avoid userspace races when probing new input devices.

Bug Fixes:

• Resolve a race where userspace could query evdev sysctl entries before they were registered when a new input device cdev appeared, causing device enumeration to fail.

Enhancements:

• Ensure sysctl context is freed if character device creation fails after sysctl registration to prevent resource leaks.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adjusts evdev device registration order so sysctl entries are created before the character device node, closing a userspace race, and ensures sysctl context is freed on cdev creation failure.

Sequence diagram for updated evdev device registration and userspace sysctl access

sequenceDiagram
    participant KernelEvdev
    participant Sysctl
    participant Cdev
    participant UserspaceLib

    KernelEvdev->>KernelEvdev: evdev_register_common
    KernelEvdev->>Sysctl: evdev_sysctl_create
    KernelEvdev->>Cdev: evdev_cdev_create
    UserspaceLib->>KernelEvdev: sysctlbyname
    KernelEvdev-->>UserspaceLib: sysctl values from kern.evdev.input.N.*

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Flow diagram for evdev_register_common error handling with sysctl_ctx_free

flowchart TD
    A[evdev_register_common] --> B[evdev_sysctl_create]
    B --> C[evdev_cdev_create]
    C --> D{ret == 0?}
    D -- Yes --> E[Success]
    D -- No --> F["sysctl_ctx_free(ev_sysctl_ctx)"]
    F --> G[bail_out / return error]

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File-Level Changes

Change	Details	Files
Reorder evdev registration so sysctl entries are created before the character device node and clean up sysctl context on failure.	Call evdev_sysctl_create(evdev) before evdev_cdev_create(evdev) to ensure sysctl nodes exist when devd emits the device CREATE event On evdev_cdev_create() failure, free the previously created sysctl context with sysctl_ctx_free(&evdev->ev_sysctl_ctx) before bailing out Add an explanatory comment documenting the userspace race between cdev creation and sysctl availability	sys/dev/evdev/evdev.c

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[github-actions]

Thank you for taking the time to contribute to FreeBSD!
There is an issue that needs to be fixed:

• Missing Signed-off-by lines^9756a73

Please review CONTRIBUTING.md, then update and push your branch again.

[sourcery-ai]

Hey - I've left some high level feedback:

• Now that sysctls are created before the cdev, consider ensuring sysctl_ctx_free(&evdev->ev_sysctl_ctx) is called on all subsequent failure paths in evdev_register_common() (not just the evdev_cdev_create() error case) to avoid leaking the sysctl context when later steps fail.
• If feasible, it may be safer for evdev_sysctl_create() to return an error code on failure instead of void, allowing evdev_register_common() to bail out early and cleanly roll back the partially initialized sysctl context.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Now that sysctls are created before the cdev, consider ensuring `sysctl_ctx_free(&evdev->ev_sysctl_ctx)` is called on all subsequent failure paths in `evdev_register_common()` (not just the `evdev_cdev_create()` error case) to avoid leaking the sysctl context when later steps fail.
- If feasible, it may be safer for `evdev_sysctl_create()` to return an error code on failure instead of `void`, allowing `evdev_register_common()` to bail out early and cleanly roll back the partially initialized sysctl context.

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[ericbsd]

@emaste I would like your opinion on this patch when you have time to look at it.

[ericbsd]

I need to think more about it. I just found an issue.